Automatic clutch with very slow speed

ABSTRACT

Disclosed is an automatic clutch intended for use in an engine-transmission unit of a vehicle. When starting up, the clutch transmits first a high torque for a very slow speed, which is then reduced after a set lapse of time if a threshold value is exceeded.

BACKGROUND OF THE INVENTION

The present invention concerns an automatic control of a clutch in thedrive train of a motor vehicle, having a transmission shifted by thedriver between different transmission stages or gears and an enginecontrolled by the driver by means of a control element, for example agas pedal. The clutch is automatically set by a motorized adjustingunit, actuated by the control, to a creeping torque at low travellingspeed or when the vehicle is stationary and the transmission stage hasbeen selected, the brake is unactuated and the control element is notactuated.

In motor vehicles with customary internal combustion engines, atransmission must be arranged in the drive train to allow thetransmission ratio between the speed of the vehicle engine and the speedof the drive wheels to be changed according to the respective travellingspeed and loading of the vehicle. In customary manually shiftedtransmissions, during the change of a transmission stage the power flowbetween engine and drive wheels has to be interrupted by releasing theclutch.

When starting the vehicle, the clutch must operate with slip, since theaforementioned transmission is not able to operate steplessly andconventional vehicle engines, in particular internal combustion engines,can only operate and deliver adequate power above a minimum speed.

It is known in principle to use automatic clutches for this purpose sothat a clutch is automatically released when changing a transmissionstage and is subsequently re-engaged. In starting situations, the clutchinitially transmits only a limited torque, i.e. the creeping torque,which is adequate for making the vehicle start to slowly creep forwardunder normal driving conditions. If the vehicle is then accelerated bycorresponding actuation of the gas pedal, the torque which can betransmitted by the clutch increases, so that, depending on therespective operating parameters, at a varying level of engine speed theclutch can transmit a torque which is above the engine torque.

It is known from EP 03 75 162 B1 to allow the automatic control of theclutch also to operate in dependence on the brake actuation in acreeping phase of the vehicle.

SUMMARY OF THE INVENTION

The object of the invention is thus to optimize the control of theclutch in the creeping phase.

This object is achieved according to the invention by initially settinga high creeping torque, at low travelling speed or when the vehicle isstationary, the transmission stage has been selected, the brake isunactuated and the control element is not actuated. The high creepingtorque is automatically reduced after a predetermined time period if thebrake continues to be unactuated and the gas pedal is not actuated.

In particular, the relatively high creeping torque can be initially setduring starting, even after ending a brake actuation.

The invention is based on the general idea of controlling the clutch atthe beginning of a starting situation, i.e. after selecting atransmission stage and ending a brake actuation and with the gas pedalnot actuated, initially to deliver a relatively high creeping torque, inorder to ensure that the vehicle can start reliably and comparativelyrapidly. Should the gas pedal continue to remain unactuated within thepredetermined time period, this is an indication that this is not a"normal" starting situation and the torque effective for driving thevehicle should be reduced. This at the same time protects the clutchagainst excessive wear. This applies in particular if the driver shouldhold a stationary or virtually stationary vehicle on an incline just byusing the creeping torque of the clutch.

According to a preferred embodiment of the invention, the reduction inthe creeping torque may be relinquished if a threshhold value for thetravelling speed has been exceeded. This is because a higher travellingspeed often indicates that a starting phase is unlikely to be terminatedby the driver. Furthermore, it is ensured on inclines that the enginecan, if required, have a braking effect even at relatively lowtravelling speed.

In addition or alternatively, it may be envisaged to monitor thedifference in speed between the input and output of the clutch and notto reduce the creeping torque if the input and output of the clutch havereached speeds which are approaching one another or the same as oneanother. It is virtually inevitable that such rotational speedconditions have the consequence that the vehicle is running at a highertravelling speed, since an automatic electronic engine control customaryin modern engines ensures virtually always that the engine, andconsequently the clutch input, rotate at a minimum speed.

Otherwise, with regard to preferred features of the invention, referenceis made to the claims and the following explanation of the drawing, onthe basis of which a particularly preferred embodiment of the inventionis described.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing, the single Figure shows a schematized representation ofa drive train of a motor vehicle as well as the components essential forthe clutch control.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An internal combustion engine 1 is connected in drive terms via anautomatically actuated clutch 2 with a transmission 3, the transmissionstages or gears of which are changed by manual actuation of a shiftlever 4, and a drive shaft 5, for example a cardan shaft, to drivewheels 6 of a motor vehicle, otherwise not represented in any moredetail.

The actuation of the clutch 2 takes place automatically by means of amotorized adjusting unit 7, which is actuated by a control circuit 8.The control circuit 8 takes into account a variety of parameters and isconnected for this purpose to an extensive system of sensors.

The system of sensors comprises a sensor arrangement 9, which isassigned to the transmission 3 or the shift lever 4 and senses thepositions and/or movements of the latter and consequently registers therespectively selected transmission stage or the respectively selectedgear. The position of an element serving for controlling the power ofthe engine 1, for example a gas pedal actuated by the driver, isregistered by a sensor 10. A displacement pickup 11 senses the travel ofthe adjusting unit 7 and consequently a parameter which is analogous tothe value of the torque which can be transmitted by the automatic clutch2. Furthermore, the control circuit 8 is connected to an engine control12, the signals of which reproduce, inter alia, the speed of the engine,the torque of the engine 1 and an actuation of a control element for thepower of the engine 1, for example the actuation of a gas pedal by thedriver. A signalling device 13 registers whether a service brake of thevehicle is actuated. This signalling device 13 may be, for example, abrake light switch, by means of which the brake lights are controlledwhen the service brake is actuated. The wheel speeds, and consequentlythe travelling speed of the vehicle, are sensed by means of speedpickups 14, which are assigned to the vehicle wheels. These speedpickups 14 often also have the function of providing the necessaryinformation on the turning of the wheels for an anti-lock brakingsystem.

On the basis of the exchange of information with the engine control 12,the control circuit 8 can determine the torque transmitted in each caseby the clutch 2 in dependence on the position of the adjusting unit 7.At constant travelling speed, the following applies for the torque M_(K)transmitted by the clutch 2:

    M.sub.K =M.sub.mot -J.sub.mot dw.sub.Mot /dt.

where M_(mot) is the torque generated by the engine 1, which is detectedby the engine control 12, J_(mot) is the moment of inertia of the engine1, which is predetermined by the design of the engine 1, and w_(Mot) isthe speed of the engine 1. t denotes time.

Since all engine-related variables can be sensed by the engine control12 and it can be detected from the signals of the speed pickups 14whether the vehicle is travelling at approximately constant speed, thecontrol circuit 8 can often "detect" on the basis of its interactionwith the engine control 12 and the speed pickups 14 the respectiveclutch torque M_(K). In addition, the control circuit 8 knows from thesignals of the displacement pickup 11 the position of the adjusting unit7, so that the control circuit 8 can also often determine or update theproportionality between the clutch torque M_(K) and the travel of theadjusting unit 7. As a result, the control circuit 8 thus "knows" thetransmissible torque respectively set at the clutch 2.

In a starting situation, i.e. when the vehicle is stationary or at verylow travelling speed, with an unactuated vehicle brake and the gas pedalor the like not actuated, the control circuit 8 initially sets theadjusting unit 7 such that the clutch 2 transmits a comparatively highcreeping torque and the vehicle has a pronounced creeping tendency. Ifthe gas pedal continues not to be actuated and the vehicle brake isunactuated, this state is maintained only for a predetermined limitedtime period, for example a few seconds. Thereafter, the torque which canbe transmitted by the clutch 2 is reduced, thereby also reducing thetendency of the vehicle to creep.

Should the vehicle brake then be actuated, on ending of the brakeactuation and with an unactuated gas pedal and the transmission stageselected, initially the high creeping torque can in turn be set and thenreduced again, if appropriate, after the aforementioned time period.

Should the vehicle exceed a threshold value for the travelling speedduring the time period with the high creeping torque, a reduction in thecreeping torque may be relinquished.

We claim:
 1. An automatic control of a clutch in the drive train of amotor vehicle comprising a transmission shifted by a driver betweendifferent transmission stages or gears and an engine controlled by thedriver by a control element, the clutch being automatically set by amotorized adjusting unit, actuated by the control, to a creeping torqueat low travelling speed or when the vehicle is stationary and thetransmission stage has been selected, a brake is unactuated and thecontrol element is not actuated,wherein a high creeping torque isinitially set, at low travelling speed or when the vehicle isstationary, the drive position has been selected, the brake isunactuated and the control element is not actuated, the high creepingtorque being automatically reduced after a predetermined time periodwhen the brake continues to be unactuated and the control element is notactuated.
 2. The control as claimed in claim 1, wherein, after brakeactuation, the high creeping torque is once again initially set.
 3. Thecontrol as claimed in claim 2, wherein the clutch is released onactuation of the brake if the travelling speed of the vehicle fallsbelow a low threshold value.
 4. The control as claimed in claim 3,wherein a reduction in the creeping torque is relinquished if athreshold value for the travelling speed is exceeded during thepredetermined time period.
 5. The control as claimed in claim 4, whereinthe reduction in the creeping torque is relinquished if the input andoutput of the clutch have reached speeds which are approaching oneanother or the same as one another.
 6. The control as claimed in claim3, wherein a reduction in the creeping torque is relinquished if theinput and output of the clutch have reached speeds which are approachingone another or the same as one another.
 7. The control as claimed inclaim 2, wherein a reduction in the creeping torque is relinquished if athreshold value for the travelling speed is exceeded during thepredetermined time period.
 8. The control as claimed in claim 7, whereinthe reduction in the creeping torque is relinquished if the input andoutput of the clutch have reached speeds which are approaching oneanother or the same as one another.
 9. The control as claimed in claim2, wherein a reduction in the creeping torque is relinquished if theinput and output of the clutch have reached speeds which are approachingone another or the same as one another.
 10. The control as claimed inclaim 1, wherein a reduction in the creeping torque is relinquished if athreshold value for the travelling speed is exceeded during thepredetermined time period.
 11. The control as claimed in claim 10,wherein the reduction in the creeping torque is relinquished if theinput and output of the clutch have reached speeds which are approachingone another or the same as one another.
 12. The control as claimed inclaim 1, wherein a reduction in the creeping torque is relinquished ifthe input and output of the clutch have reached speeds which areapproaching one another or the same as one another.
 13. An automaticcontrol of a clutch in the drive train of a motor vehicle comprising atransmission shifted by a driver between different transmission stagesor gears and an engine controlled by the driver by a control element,the clutch being automatically set by a motorized adjusting unit,actuated by the control, to a creeping torque at low travelling speed orwhen the vehicle is stationary and the transmission stage has beenselected, a brake is unactuated and the control element is notactuated,wherein a relatively high creeping torque, envisaged for anormal starting situation and allowing the vehicle to start reliably andcomparatively rapidly, is initially set, at low travelling speed or whenthe vehicle is stationary, the drive position has been selected, thebrake is unactuated and the control element is not actuated, and, aftera predetermined time period, when the brake continues to be unactuatedand the control element is not actuated, is automatically reduced, witha corresponding reduction in a creeping tendency of the vehicle.
 14. Thecontrol as claimed in claim 13, wherein, after brake actuation, the highcreeping torque is once again initially set.
 15. The control as claimedin claim 14, wherein the clutch is released on actuation of the brake ifthe travelling speed of the vehicle falls below a low threshold value.16. The control as claimed in claim 13, wherein a reduction in thecreeping torque is relinquished if a threshold value for the travellingspeed is exceeded during the predetermined time period.
 17. The controlas claimed in claim 13, wherein a reduction in the creeping torque isrelinquished if the input and output of the clutch have reached speedswhich are approaching one another or the same as one another.